Vehicles equipped whit a 4 speed automatic transmission may develop a harsh 1-2 shift and/or illumination of the Check Engine Light with code P1870 stored. This can be caused by wear of the bore for the TCC isolator and regulator valves in the valve body. This condition does not commonly occur until the transmission reaches normal operating temperature. If the valve body is worn, replacement will be necessary to correct this concern.
Check Engine Light With Code P1870 on GMC Savana 1500
Average mileage: 229,000 (229,000–229,000)
7 people reported this problem
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It always shifted hard since it was new but now it triggers check engine light. The light comes and goes and it is worse in hot weather. I cant get it E checked now for plates. runs great but i dont want to spend the money for a new transmission on a van this old with this many miles on it. The van runs great it drives just fine. I dont notice any shifting problems other than rarely it will shift hard between first and second making the engine light come on. It happens more when I drive slow or easy rather than when i drive it hard. I thought about replacing the seleniods but Im not sure if that will solve the problem. Nothing else wrong with the van.